Input device receiver with delta-sigma modulator

ABSTRACT

A processing system, and associated input device and method are disclosed suitable for reducing a receiver size within the input device. The processing system comprises a delta-sigma modulator comprising one or more input nodes configured to receive a signal based on a sensor signal received from at least a first sensor electrode of the plurality of sensor electrodes. The delta-sigma modulator further comprises an integrator coupled with the one or more input nodes and configured to produce an integration signal, a quantizer coupled with an output of the integrator and configured to quantize the integration signal, and a feedback digital-to-analog converter (DAC) controlled based by the quantizer. The processing system further comprises a digital filter coupled with an output of the delta-sigma modulator and configured to mitigate a quantization noise of the quantizer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/199,276, filed Jun. 30, 2016, entitled “INPUT DEVICE RECEIVER WITHDELTA-SIGMA MODULATOR”, U.S. Pat. No. 10,061,415, which is hereinincorporated by reference in its entirety.

FIELD

Embodiments of the present invention generally relate to techniques foroperating an input device having a display device with an integratedsensing device.

DESCRIPTION OF THE RELATED ART

Input devices including proximity sensor devices (also commonly calledtouchpads or touch sensor devices) are widely used in a variety ofelectronic systems. A proximity sensor device typically includes asensing region, often demarked by a surface, in which the proximitysensor device determines the presence, location and/or motion of one ormore input objects. Proximity sensor devices may be used to provideinterfaces for the electronic system. For example, proximity sensordevices are often used as input devices for larger computing systems(such as opaque touchpads integrated in, or peripheral to, notebook ordesktop computers). Proximity sensor devices are also often used insmaller computing systems (such as touch screens integrated in cellularphones).

SUMMARY

One embodiment described herein is a processing system for an inputdevice comprising a plurality of sensor electrodes. The processingsystem comprises a delta-sigma modulator comprising one or more inputnodes configured to receive a signal based on a sensor signal receivedfrom at least a first sensor electrode of the plurality of sensorelectrodes, and an integrator coupled with the one or more input nodesand configured to produce an integration signal. The delta-sigmamodulator further comprises a quantizer coupled with an output of theintegrator and configured to quantize the integration signal and afeedback digital-to-analog converter (DAC) controlled based by thequantizer. The processing system further comprises a digital filtercoupled with an output of the delta-sigma modulator and configured tomitigate a quantization noise of the quantizer.

Another embodiment described herein is an input device, comprising aplurality of sensor electrodes, and a processing system coupled with theplurality of sensor electrodes. The processing system comprises adelta-sigma modulator comprising one or more input nodes configured toreceive a signal based on a sensor signal received from at first sensorelectrode of the plurality of sensor electrodes. The delta-sigmamodulator further comprises an integrator coupled with the one or moreinput nodes and configured to produce an integration signal, a quantizercoupled with an output of the integrator and configured to quantize theintegration signal, and a feedback digital-to-analog converter (DAC)controlled based by the quantizer. The processing system furthercomprises a digital filter coupled with an output of the delta-sigmamodulator and configured to mitigate a quantization noise of thequantizer.

Another embodiment described herein is a method comprising receiving, atone or more input nodes, a sensor signal from a first sensor electrodeof a plurality of sensor electrodes. The method further comprisesintegrating a signal based on the sensor signal to produce anintegration signal, and quantizing the integration signal. The methodfurther comprises controlling a feedback digital-to-analog converter(DAC) based on the quantization of the integration signal, the feedbackDAC coupled with the one or more input nodes. The method furthercomprises mitigating a quantization noise using a digital filter.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, may admit to other equally effective embodiments.

FIG. 1 is a schematic block diagram of an input device, according to oneembodiment.

FIGS. 2 and 3 illustrate portions of exemplary sensor electrodearrangements, according to one embodiment.

FIG. 4 illustrates a block diagram of an exemplary input device,according to one embodiment.

FIG. 5 illustrates a schematic block diagram of an exemplary inputdevice, according to one embodiment.

FIG. 6 is an exemplary method of processing signals received from asensor electrode, according to one embodiment.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation. The drawings referred to here should not beunderstood as being drawn to scale unless specifically noted. Also, thedrawings are often simplified and details or components omitted forclarity of presentation and explanation. The drawings and discussionserve to explain principles discussed below, where like designationsdenote like elements.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the disclosure or the application and uses of thedisclosure. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding background,summary, or in the following detailed description.

As input devices become more complex and include increasing numbers ofsensor electrodes, the processing demands on the processing system aresimilarly increased. To suitably process the input signals received fromthe sensor electrodes within other system constraints, the processingsystem tends to require at least one of (1) more area for additionalprocessing circuitry for the sensor electrodes, (2) reduced-sizeprocessing circuitry for a given area, and (3) more time for processingthe received input signals. However, as input device functionalitycontinues to increase within the same (or smaller) packaging, increasingthe area allotted for processing circuitry in some cases is notfeasible. Moreover, providing more area for additional processingcircuitry may increase production costs. Further, for input deviceshaving integrated display devices, higher resolution displays tend torequire more time for display updating. As a result, in some cases,allotting more time for processing received input signals from sensorelectrodes is not feasible.

Embodiments described herein generally include a processing system andassociated input device and method for processing signals received froma sensor electrode. More specifically, the processing system comprises adelta-sigma modulator comprising an integrator, quantizer, feedbackdigital-to-analog converter (DAC) and common-mode feedback arrangement.In some embodiments, the delta-sigma modulator is included within ananalog front-end (AFE) or other receiver circuitry of the processingsystem. In some embodiments, the delta-sigma modulator comprises adifferential first-order continuous time passive delta-sigma modulator.Collectively, the components of the delta-sigma modulator result in anAFE having a significantly smaller size than conventional AFEs.

Exemplary Input Device Implementations

FIG. 1 is a schematic block diagram of an input device 100, inaccordance with embodiments of the present technology. In variousembodiments, input device 100 comprises a display device integrated witha sensing device. The input device 100 may be configured to provideinput to an electronic system 150. As used in this document, the term“electronic system” (or “electronic device”) broadly refers to anysystem capable of electronically processing information. Somenon-limiting examples of electronic systems include personal computersof all sizes and shapes, such as desktop computers, laptop computers,netbook computers, tablets, web browsers, e-book readers, and personaldigital assistants (PDAs). Additional example electronic systems includecomposite input devices, such as physical keyboards that include inputdevice 100 and separate joysticks or key switches. Further exampleelectronic systems include peripherals such as data input devices(including remote controls and mice), and data output devices (includingdisplay screens and printers). Other examples include remote terminals,kiosks, and video game machines (e.g., video game consoles, portablegaming devices, and the like). Other examples include communicationdevices (including cellular phones, such as smart phones), and mediadevices (including recorders, editors, and players such as televisions,set-top boxes, music players, digital photo frames, and digitalcameras). Additionally, the electronic system could be a host or a slaveto the input device.

The input device 100 can be implemented as a physical part of theelectronic system, or can be physically separate from the electronicsystem. As appropriate, the input device 100 may communicate with partsof the electronic system using any one or more of the following: buses,networks, and other wired or wireless interconnections. Examples includeI²C, SPI, PS/2, Universal Serial Bus (USB), Bluetooth, RF, and IRDA.

In FIG. 1, the input device 100 is shown as a proximity sensor device(also often referred to as a “touchpad” or a “touch sensor device”)configured to sense input provided by one or more input objects 140 in asensing region 170. Example input objects include fingers and styli, asshown in FIG. 1.

Sensing region 170 encompasses any space above, around, in and/or nearthe input device 100 in which the input device 100 is able to detectuser input (e.g., user input provided by one or more input objects 140).The sizes, shapes, and locations of particular sensing regions may varywidely from embodiment to embodiment. In some embodiments, the sensingregion 170 extends from a surface of the input device 100 in one or moredirections into space until signal-to-noise ratios prevent sufficientlyaccurate object detection. The distance to which this sensing region 170extends in a particular direction, in various embodiments, may be on theorder of less than a millimeter, millimeters, centimeters, or more, andmay vary significantly with the type of sensing technology used and theaccuracy desired. Thus, some embodiments sense input that comprises nocontact with any surfaces of the input device 100, contact with an inputsurface (e.g. a touch surface) of the input device 100, contact with aninput surface of the input device 100 coupled with some amount ofapplied force or pressure, and/or a combination thereof. In variousembodiments, input surfaces may be provided by surfaces of casingswithin which the sensor electrodes reside, by face sheets applied overthe sensor electrodes or any casings, etc. In some embodiments, thesensing region 170 has a rectangular shape when projected onto an inputsurface of the input device 100.

The input device 100 may utilize any combination of sensor componentsand sensing technologies to detect user input in the sensing region 170.The input device 100 comprises a plurality of sensor electrodes 120 fordetecting user input. The input device 100 may include one or moresensor electrodes 120 that are combined to form sensor electrodes. Asseveral non-limiting examples, the input device 100 may use capacitive,elastive, resistive, inductive, magnetic acoustic, ultrasonic, and/oroptical techniques.

Some implementations are configured to provide images that span one,two, three, or higher dimensional spaces. Some implementations areconfigured to provide projections of input along particular axes orplanes.

In some resistive implementations of the input device 100, a flexibleand conductive first layer is separated by one or more spacer elementsfrom a conductive second layer. During operation, one or more voltagegradients are created across the layers. Pressing the flexible firstlayer may deflect it sufficiently to create electrical contact betweenthe layers, resulting in voltage outputs reflective of the point(s) ofcontact between the layers. These voltage outputs may be used todetermine positional information.

In some inductive implementations of the input device 100, one or moresensor electrodes 120 pickup loop currents induced by a resonating coilor pair of coils. Some combination of the magnitude, phase, andfrequency of the currents may then be used to determine positionalinformation.

In some capacitive implementations of the input device 100, voltage orcurrent is applied to create an electric field. Nearby input objectscause changes in the electric field, and produce detectable changes incapacitive coupling that may be detected as changes in voltage, current,or the like.

Some capacitive implementations utilize arrays or other regular orirregular patterns of capacitive sensor electrodes 120 to createelectric fields. In some capacitive implementations, separate sensorelectrodes 120 may be ohmically shorted together to form larger sensorelectrodes. Some capacitive implementations utilize resistive sheets,which may be uniformly resistive.

As discussed above, some capacitive implementations utilize“self-capacitance” (or “absolute capacitance”) sensing methods based onchanges in the capacitive coupling between sensor electrodes 120 and aninput object. In one embodiment, processing system 110 is configured todrive a voltage with known amplitude onto the sensor electrode 120 andmeasure the amount of charge required to charge the sensor electrode tothe driven voltage. In other embodiments, processing system 110 isconfigured to drive a known current and measure the resulting voltage.In various embodiments, an input object near the sensor electrodes 120alters the electric field near the sensor electrodes 120, thus changingthe measured capacitive coupling. In one implementation, an absolutecapacitance sensing method operates by modulating sensor electrodes 120with respect to a reference voltage (e.g. system ground) using amodulated signal, and by detecting the capacitive coupling between thesensor electrodes 120 and input objects 140.

Additionally as discussed above, some capacitive implementations utilize“mutual capacitance” (or “transcapacitance”) sensing methods based onchanges in the capacitive coupling between sensing electrodes. Invarious embodiments, an input object 140 near the sensing electrodesalters the electric field between the sensing electrodes, thus changingthe measured capacitive coupling. In one implementation, atranscapacitive sensing method operates by detecting the capacitivecoupling between one or more transmitter sensing electrodes (also“transmitter electrodes”) and one or more receiver sensing electrodes(also “receiver electrodes”) as further described below. Transmittersensing electrodes may be modulated relative to a reference voltage(e.g., system ground) to transmit a transmitter signals. Receiversensing electrodes may be held substantially constant relative to thereference voltage to facilitate receipt of resulting signals. Aresulting signal may comprise effect(s) corresponding to one or moretransmitter signals, and/or to one or more sources of environmentalinterference (e.g. other electromagnetic signals). Sensing electrodesmay be dedicated transmitter electrodes or receiver electrodes, or maybe configured to both transmit and receive.

In FIG. 1, the processing system 110 is shown as part of the inputdevice 100. The processing system 110 is configured to operate thehardware of the input device 100 to detect input in the sensing region170. The processing system 110 comprises parts of or all of one or moreintegrated circuits (ICs) and/or other circuitry components. Forexample, a processing system for a mutual capacitance sensor device maycomprise transmitter circuitry configured to transmit signals withtransmitter sensor electrodes, and/or receiver circuitry configured toreceive signals with receiver sensor electrodes. In some embodiments,the processing system 110 also comprises electronically-readableinstructions, such as firmware code, software code, and/or the like. Insome embodiments, components composing the processing system 110 arelocated together, such as near sensor electrode(s) 120 of the inputdevice 100. In other embodiments, components of processing system 110are physically separate with one or more components close to sensorelectrode(s) 120 of input device 100, and one or more componentselsewhere. For example, the input device 100 may be a peripheral coupledto a desktop computer, and the processing system 110 may comprisesoftware configured to run on a central processing unit of the desktopcomputer and one or more ICs (perhaps with associated firmware) separatefrom the central processing unit. As another example, the input device100 may be physically integrated in a phone, and the processing system110 may comprise circuits and firmware that are part of a main processorof the phone. In some embodiments, the processing system 110 isdedicated to implementing the input device 100. In other embodiments,the processing system 110 also performs other functions, such asoperating display screens, driving haptic actuators, etc.

The processing system 110 may be implemented as a set of modules thathandle different functions of the processing system 110. Each module maycomprise circuitry that is a part of the processing system 110,firmware, software, or a combination thereof. In various embodiments,different combinations of modules may be used. Example modules includehardware operation modules for operating hardware such as sensorelectrodes and display screens, data processing modules for processingdata such as sensor signals and positional information, and reportingmodules for reporting information. Further example modules includesensor operation modules configured to operate sensor electrodes 120 todetect input, identification modules configured to identify gesturessuch as mode changing gestures, and mode changing modules for changingoperation modes. Processing system 110 may also comprise one or morecontrollers.

In some embodiments, the processing system 110 responds to user input(or lack of user input) in the sensing region 170 directly by causingone or more actions. Example actions include changing operation modes,as well as GUI actions such as cursor movement, selection, menunavigation, and other functions. In some embodiments, the processingsystem 110 provides information about the input (or lack of input) tosome part of the electronic system (e.g. to a central processing systemof the electronic system that is separate from the processing system110, if such a separate central processing system exists). In someembodiments, some part of the electronic system processes informationreceived from the processing system 110 to act on user input, such as tofacilitate a full range of actions, including mode changing actions andGUI actions.

For example, in some embodiments, the processing system 110 operates thesensor electrode(s) 120 of the input device 100 to produce electricalsignals indicative of input (or lack of input) in the sensing region170. The processing system 110 may perform any appropriate amount ofprocessing on the electrical signals in producing the informationprovided to the electronic system. For example, the processing system110 may digitize analog electrical signals obtained from the sensorelectrodes 120. As another example, the processing system 110 mayperform filtering or other signal conditioning. As yet another example,the processing system 110 may subtract or otherwise account for abaseline, such that the information reflects a difference between theelectrical signals and the baseline. As yet further examples, theprocessing system 110 may determine positional information, recognizeinputs as commands, recognize handwriting, and the like.

“Positional information” as used herein broadly encompasses absoluteposition, relative position, velocity, acceleration, and other types ofspatial information. Exemplary “zero-dimensional” positional informationincludes near/far or contact/no contact information. Exemplary“one-dimensional” positional information includes positions along anaxis. Exemplary “two-dimensional” positional information includesmotions in a plane. Exemplary “three-dimensional” positional informationincludes instantaneous or average velocities in space. Further examplesinclude other representations of spatial information. Historical dataregarding one or more types of positional information may also bedetermined and/or stored, including, for example, historical data thattracks position, motion, or instantaneous velocity over time.

In some embodiments, the input device 100 is implemented with additionalinput components that are operated by the processing system 110 or bysome other processing system. These additional input components mayprovide redundant functionality for input in the sensing region 170, orsome other functionality. FIG. 1 shows buttons 130 near the sensingregion 170 that can be used to facilitate selection of items using theinput device 100. Other types of additional input components includesliders, balls, wheels, switches, and the like. Conversely, in someembodiments, the input device 100 may be implemented with no other inputcomponents.

In some embodiments, the input device 100 comprises a touch screeninterface, and the sensing region 170 overlaps at least part of anactive area of a display screen of the display device 160. For example,the input device 100 may comprise substantially transparent sensorelectrodes 120 overlaying the display screen and provide a touch screeninterface for the associated electronic system. The display screen maybe any type of dynamic display capable of displaying a visual interfaceto a user, and may include any type of light emitting diode (LED),organic LED (OLED), cathode ray tube (CRT), liquid crystal display(LCD), plasma, electroluminescence (EL), or other display technology.The input device 100 and the display device 160 may share physicalelements. For example, some embodiments may utilize some of the sameelectrical components for displaying and sensing. As another example,the display device 160 may be operated in part or in total by theprocessing system 110.

It should be understood that while many embodiments of the presenttechnology are described in the context of a fully functioningapparatus, the mechanisms of the present technology are capable of beingdistributed as a program product (e.g., software) in a variety of forms.For example, the mechanisms of the present technology may be implementedand distributed as a software program on information bearing media thatare readable by electronic processors (e.g., non-transitorycomputer-readable and/or recordable/writable information bearing mediareadable by the processing system 110). Additionally, the embodiments ofthe present technology apply equally regardless of the particular typeof medium used to carry out the distribution. Examples ofnon-transitory, electronically readable media include various discs,memory sticks, memory cards, memory modules, and the like.Electronically readable media may be based on flash, optical, magnetic,holographic, or any other storage technology.

Exemplary Sensor Electrode Arrangements

FIGS. 2 and 3 illustrate portions of exemplary sensor electrodearrangements, according to embodiments described herein. Specifically,arrangement 200 (FIG. 2) illustrates a portion of a pattern of sensorelectrodes configured to sense in a sensing region 170 associated withthe pattern, according to several embodiments. For clarity ofillustration and description, FIG. 2 shows the sensor electrodes in apattern of simple rectangles, and does not show various associatedcomponents. This pattern of sensing electrodes comprises a firstplurality of sensor electrodes 205 (e.g., 205-1, 205-2, 205-3, 205-4),and a second plurality of sensor electrodes 215 (e.g., 215-1, 215-2,215-3, 215-4). The sensor electrodes 205, 215 are each examples of thesensor electrodes 120 discussed above. In one embodiment, processingsystem 110 operates the first plurality of sensor electrodes 205 as aplurality of transmitter electrodes, and the second plurality of sensorelectrodes 215 as a plurality of receiver electrodes. In anotherembodiment, processing system 110 operates the first plurality of sensorelectrodes 205 and the second plurality of sensor electrodes 215 asabsolute capacitive sensing electrodes.

The first plurality of sensor electrodes 205 and the second plurality ofsensor electrodes 215 are typically ohmically isolated from each other.That is, one or more insulators separate the first plurality of sensorelectrodes 205 and the second plurality of sensor electrodes 215 andprevent them from electrically shorting to each other. In someembodiments, the first plurality of sensor electrodes 205 and the secondplurality of sensor electrodes 215 may be disposed on a common layer.The pluralities of sensor electrodes 205, 215 may be electricallyseparated by insulative material disposed between them at cross-overareas; in such constructions, the first plurality of sensor electrodes205 and/or the second plurality of sensor electrodes 215 may be formedwith jumpers connecting different portions of the same electrode. Insome embodiments, the first plurality of sensor electrodes 205 and thesecond plurality of sensor electrodes 215 are separated by one or morelayers of insulative material. In some embodiments, the first pluralityof sensor electrodes 205 and the second plurality of sensor electrodes215 are separated by one or more substrates; for example, they may bedisposed on opposite sides of the same substrate, or on differentsubstrates that are laminated together.

The pluralities of sensor electrodes 205, 215 may be formed into anydesired shapes. Moreover, the size and/or shape of the sensor electrodes205 may be different than the size and/or shape of the sensor electrodes215. Additionally, sensor electrodes 205, 215 located on a same side ofa substrate may have different shapes and/or sizes. In one embodiment,the first plurality of sensor electrodes 205 may be larger (e.g., havinga larger surface area) than the second plurality of sensor electrodes215, although this is not a requirement. In other embodiments, the firstand second pluralities of sensor electrodes 205, 215 may have a similarsize and/or shape.

In one embodiment, the first plurality of sensor electrodes 205 extendssubstantially in a first direction while the second plurality of sensorelectrodes 215 extends substantially in a second direction. For example,and as shown in FIG. 2, the first plurality of sensor electrodes 205extend in one direction, while the second plurality of sensor electrodes215 extend in a direction substantially orthogonal to the sensorelectrodes 205. Other orientations are also possible (e.g., parallel orother relative orientations).

In some embodiments, both the first and second pluralities of sensorelectrodes 205, 215 are located outside of a plurality (or displaystack) of layers that together form the display device 160. One exampleof a display stack may include layers such as a lens layer, a one ormore polarizer layers, a color filter layer, one or more displayelectrodes layers, a display material layer, a thin-film transistor(TFT) glass layer, and a backlight layer. However, other arrangements ofa display stack are possible. In other embodiments, one or both of thefirst and second pluralities of sensor electrodes 205, 215 are locatedwithin the display stack, whether included as part of a display-relatedlayer or a separate layer. For example, Vcom electrodes within aparticular display electrode layer can be configured to perform bothdisplay updating and capacitive sensing.

Arrangement 300 of FIG. 3 illustrates a portion of a pattern of sensorelectrodes configured to sense in sensing region 170, according toseveral embodiments. For clarity of illustration and description, FIG. 3shows the sensor electrodes 120 in a pattern of simple rectangles anddoes not show other associated components. The exemplary patterncomprises an array of sensor electrodes 120 _(x,y) arranged in X columnsand Y rows, wherein X and Y are positive integers, although one of X andY may be zero. It is contemplated that the pattern of sensor electrodes120 may have other configurations, such as polar arrays, repeatingpatterns, non-repeating patterns, a single row or column, or othersuitable arrangement. Further, in various embodiments the number ofsensor electrodes 120 may vary from row to row and/or column to column.In one embodiment, at least one row and/or column of sensor electrodes120 is offset from the others, such it extends further in at least onedirection than the others. The sensor electrodes 120 is coupled to theprocessing system 110 and utilized to determine the presence (or lackthereof) of an input object in the sensing region 170.

In a first mode of operation, the arrangement of sensor electrodes 120(120 _(1,1), 120 _(2,1), 120 _(3,1), . . . , 120 _(X,Y)) may be utilizedto detect the presence of an input object via absolute sensingtechniques. That is, processing system 110 is configured to modulatesensor electrodes 120 to acquire measurements of changes in capacitivecoupling between the modulated sensor electrodes 120 and an input objectto determine the position of the input object. Processing system 110 isfurther configured to determine changes of absolute capacitance based ona measurement of resulting signals received with sensor electrodes 120which are modulated.

In some embodiments, the arrangement 300 includes one or more gridelectrodes (not shown) that are disposed between at least two of thesensor electrodes 120. The grid electrode(s) may at least partiallycircumscribe the plurality of sensor electrodes 120 as a group, and mayalso, or in the alternative, completely or partially circumscribe one ormore of the sensor electrodes 120. In one embodiment, the grid electrodeis a planar body having a plurality of apertures, where each aperturecircumscribes a respective one of the sensor electrodes 120. In otherembodiments, the grid electrode(s) comprise a plurality of segments thatmay be driven individually or in groups or two or more segments. Thegrid electrode(s) may be fabricated similar to the sensor electrodes120. The grid electrode(s), along with sensor electrodes 120, may becoupled to the processing system 110 utilizing conductive routing tracesand used for input object detection.

The sensor electrodes 120 are typically ohmically isolated from eachother, and are also ohmically isolated from the grid electrode(s). Thatis, one or more insulators separate the sensor electrodes 120 and gridelectrode(s) and prevent them from electrically shorting to each other.In some embodiments, the sensor electrodes 120 and grid electrode(s) areseparated by an insulative gap, which may be filled with an electricallyinsulating material, or may be an air gap. In some embodiments, thesensor electrodes 120 and the grid electrode(s) are vertically separatedby one or more layers of insulative material. In some other embodiments,the sensor electrodes 120 and the grid electrode(s) are separated by oneor more substrates; for example, they may be disposed on opposite sidesof the same substrate, or on different substrates. In yet otherembodiments, the grid electrode(s) may be composed of multiple layers onthe same substrate, or on different substrates. In one embodiment, afirst grid electrode may be formed on a first substrate (or a first sideof a substrate) and a second grid electrode may be formed on a secondsubstrate (or a second side of a substrate). For example, a first gridelectrode comprises one or more common electrodes disposed on athin-film transistor (TFT) layer of the display device 160 (FIG. 1) anda second grid electrode is disposed on the color filter glass of thedisplay device 160. The dimensions of the first and second gridelectrodes can be equal or differ in at least one dimension.

In a second mode of operation, the sensor electrodes 120 (120 _(1,1),120 _(2,1), 120 _(3,1), . . . , 120 _(X,Y)) may be utilized to detectthe presence of an input object via transcapacitive sensing techniqueswhen a transmitter signal is driven onto the grid electrode(s). That is,processing system 110 is configured to drive the grid electrode(s) witha transmitter signal and to receive resulting signals with each sensorelectrode 120, where a resulting signal comprising effects correspondingto the transmitter signal, which is utilized by the processing system110 or other processor to determine the position of the input object.

In a third mode of operation, the sensor electrodes 120 may be splitinto groups of transmitter and receiver electrodes utilized to detectthe presence of an input object via transcapacitive sensing techniques.That is, processing system 110 may drive a first group of sensorelectrodes 120 with a transmitter signal and receive resulting signalswith the second group of sensor electrodes 120, where a resulting signalcomprising effects corresponding to the transmitter signal. Theresulting signal is utilized by the processing system 110 or otherprocessor to determine the position of the input object.

The input device 100 may be configured to operate in any one of themodes described above. The input device 100 may also be configured toswitch between any two or more of the modes described above.

The areas of localized capacitive sensing of capacitive couplings may betermed “capacitive pixels,” “touch pixels,” “tixels,” etc. Capacitivepixels may be formed between an individual sensor electrode 120 and areference voltage in the first mode of operation, between the sensorelectrodes 120 and grid electrode(s) in the second mode of operation,and between groups of sensor electrodes 120 used as transmitter andreceiver electrodes (e.g., arrangement 200 of FIG. 2). The capacitivecoupling changes with the proximity and motion of input objects in thesensing region 170 associated with the sensor electrodes 120, and thusmay be used as an indicator of the presence of the input object in thesensing region of the input device 100.

In some embodiments, the sensor electrodes 120 are “scanned” todetermine these capacitive couplings. That is, in one embodiment, one ormore of the sensor electrodes 120 are driven to transmit transmittersignals. Transmitters may be operated such that one transmitterelectrode transmits at one time, or such that multiple transmitterelectrodes transmit at the same time. Where multiple transmitterelectrodes transmit simultaneously, the multiple transmitter electrodesmay transmit the same transmitter signal and thereby produce aneffectively larger transmitter electrode. Alternatively, the multipletransmitter electrodes may transmit different transmitter signals. Forexample, multiple transmitter electrodes may transmit differenttransmitter signals according to one or more coding schemes that enabletheir combined effects on the resulting signals of receiver electrodesto be independently determined. In one embodiment, multiple transmitterelectrodes may simultaneously transmit the same transmitter signal whilethe receiver electrodes receive the effects and are measured accordingto a scanning scheme.

The sensor electrodes 120 configured as receiver sensor electrodes maybe operated singly or multiply to acquire resulting signals. Theresulting signals may be used to determine measurements of thecapacitive couplings at the capacitive pixels. Processing system 110 maybe configured to receive with the sensor electrodes 120 in a scanningfashion and/or a multiplexed fashion to reduce the number ofsimultaneous measurements to be made, as well as the size of thesupporting electrical structures. In one embodiment, one or more sensorelectrodes are coupled to a receiver of processing system 110 via aswitching element such as a multiplexer or the like. In such anembodiment, the switching element may be internal to processing system110 or external to processing system 110. In one or more embodiments,the switching elements may be further configured to couple a sensorelectrode 120 with a transmitter or other signal and/or voltagepotential. In one embodiment, the switching element may be configured tocouple more than one receiver electrode to a common receiver at the sametime.

In other embodiments, “scanning” sensor electrodes 120 to determinethese capacitive couplings comprises modulating one or more of thesensor electrodes and measuring an absolute capacitance of the one orsensor electrodes. In another embodiment, the sensor electrodes may beoperated such that more than one sensor electrode is driven and receivedwith at a time. In such embodiments, an absolute capacitive measurementmay be obtained from each of the one or more sensor electrodes 120simultaneously. In one embodiment, each of the sensor electrodes 120 aresimultaneously driven and received with, obtaining an absolutecapacitive measurement simultaneously from each of the sensor electrodes120. In various embodiments, processing system 110 may be configured toselectively modulate a portion of sensor electrodes 120. For example,the sensor electrodes may be selected based on, but not limited to, anapplication running on the host processor, a status of the input device,and an operating mode of the sensing device. In various embodiments,processing system 110 may be configured to selectively shield at least aportion of sensor electrodes 120 and to selectively shield or transmitwith the grid electrode(s) 122 while selectively receiving and/ortransmitting with other sensor electrodes 120.

A set of measurements from the capacitive pixels form a “capacitiveimage” (also “capacitive frame”) representative of the capacitivecouplings at the pixels. Multiple capacitive images may be acquired overmultiple time periods, and differences between them used to deriveinformation about input in the sensing region. For example, successivecapacitive images acquired over successive periods of time can be usedto track the motion(s) of one or more input objects entering, exiting,and within the sensing region.

In any of the above embodiments, multiple sensor electrodes 120 may beganged together such that the sensor electrodes 120 are simultaneouslymodulated or simultaneously received with. As compared to the methodsdescribed above, ganging together multiple sensor electrodes may producea coarse capacitive image that may not be usable to discern precisepositional information. However, a coarse capacitive image may be usedto sense presence of an input object. In one embodiment, the coarsecapacitive image may be used to move processing system 110 or the inputdevice 100 out of a “doze” mode or low-power mode. In one embodiment,the coarse capacitive image may be used to move a capacitive sensing ICout of a “doze” mode or low-power mode. In another embodiment, thecoarse capacitive image may be used to move at least one of a host ICand a display driver out of a “doze” mode or low-power mode. The coarsecapacitive image may correspond to the entire sensor area or only to aportion of the sensor area.

The background capacitance of the input device 100 is the capacitiveimage associated with no input object in the sensing region 170. Thebackground capacitance changes with the environment and operatingconditions, and may be estimated in various ways. For example, someembodiments take “baseline images” when no input object is determined tobe in the sensing region 170, and use those baseline images as estimatesof their background capacitances. The background capacitance or thebaseline capacitance may be present due to stray capacitive couplingbetween two sensor electrodes, where one sensor electrode is driven witha modulated signal and the other is held stationary relative to systemground, or due to stray capacitive coupling between a receiver electrodeand nearby modulated electrodes. In many embodiments, the background orbaseline capacitance may be relatively stationary over the time periodof a user input gesture.

Capacitive images can be adjusted for the background capacitance of theinput device 100 for more efficient processing. Some embodimentsaccomplish this by “baselining” measurements of the capacitive couplingsat the capacitive pixels to produce a “baselined capacitive image.” Thatis, some embodiments compare the measurements forming a capacitanceimage with appropriate “baseline values” of a “baseline image”associated with those pixels, and determine changes from that baselineimage.

In some touch screen embodiments, one or more of the sensor electrodes120 comprise one or more display electrodes used in updating the displayof the display screen. The display electrodes may comprise one or moreelements of the active matrix display such as one or more segments of asegmented Vcom electrode (common electrode(s)), a source drive line,gate line, an anode sub-pixel electrode or cathode pixel electrode, orany other suitable display element. These display electrodes may bedisposed on an appropriate display screen substrate. For example, thecommon electrodes may be disposed on the a transparent substrate (aglass substrate, TFT glass, or any other transparent material) in somedisplay screens (e.g., In-Plane Switching (IPS), Fringe Field Switching(FFS) or Plane to Line Switching (PLS) Organic Light Emitting Diode(OLED)), on the bottom of the color filter glass of some display screens(e.g., Patterned Vertical Alignment (PVA) or Multi-domain VerticalAlignment (MVA)), over an emissive layer (OLED), etc. In suchembodiments, the display electrode can also be referred to as a“combination electrode,” since it performs multiple functions. Invarious embodiments, each of the sensor electrodes 120 comprises one ormore common electrodes. In other embodiments, at least two sensorelectrodes 120 may share at least one common electrode. While thefollowing description may describe that sensor electrodes 120 and/orgrid electrode(s) comprise one or more common electrodes, various otherdisplay electrodes as describe above may also be used in conjunctionwith the common electrode or as an alternative to the common electrodes.In various embodiments, the sensor electrodes 120 and grid electrode(s)comprise the entire common electrode layer (Vcom electrode).

In various touch screen embodiments, the “capacitive frame rate” (therate at which successive capacitive images are acquired) may be the sameor be different from that of the “display frame rate” (the rate at whichthe display image is updated, including refreshing the screen toredisplay the same image). In various embodiments, the capacitive framerate is an integer multiple of the display frame rate. In otherembodiments, the capacitive frame rate is a fractional multiple of thedisplay frame rate. In yet further embodiments, the capacitive framerate may be any fraction or integer multiple of the display frame rate.In one or more embodiments, the display frame rate may change (e.g., toreduce power or to provide additional image data such as a 3D displayinformation) while touch frame rate maintains constant. In otherembodiment, the display frame rate may remain constant while the touchframe rate is increased or decreased.

Continuing to refer to FIG. 3, the processing system 110 coupled to thesensor electrodes 120 includes a sensor module 310 and optionally, adisplay driver module 320. The sensor module 310 includes circuitryconfigured to drive at least one of the sensor electrodes 120 forcapacitive sensing during periods in which input sensing is desired. Inone embodiment, the sensor module 310 is configured to drive a modulatedsignal onto the at least one sensor electrode 120 to detect changes inabsolute capacitance between the at least one sensor electrode and aninput object. In another embodiment, the sensor module 310 is configuredto drive a transmitter signal onto the at least one sensor electrode 120to detect changes in a transcapacitance between the at least one sensorelectrode and another sensor electrode 120. The modulated andtransmitter signals are generally varying voltage signals comprising aplurality of voltage transitions over a period of time allocated forinput sensing. In various embodiments, the sensor electrodes 120 and/orgrid electrode(s) may be driven differently in different modes ofoperation. In one embodiment, the sensor electrodes 120 and/or gridelectrode(s) may be driven with signals (modulated signals, transmittersignals and/or shield signals) that may differ in any one of phase,amplitude, and/or shape. In various embodiments, the modulated signaland transmitter signal are similar in at least one shape, frequency,amplitude, and/or phase. In other embodiments, the modulated signal andthe transmitter signals are different in frequency, shape, phase,amplitude, and phase. The sensor module 310 may be selectively coupledone or more of the sensor electrodes 120 and/or the grid electrode(s).For example, the sensor module 310 may be coupled selected portions ofthe sensor electrodes 120 and operate in either an absolute ortranscapacitive sensing mode. In another example, the sensor module 310may be a different portion of the sensor electrodes 120 and operate ineither an absolute or transcapacitive sensing mode. In yet anotherexample, the sensor module 310 may be coupled to all the sensorelectrodes 120 and operate in either an absolute or transcapacitivesensing mode.

The sensor module 310 is configured to operate the grid electrode(s) asa shield electrode that may shield sensor electrodes 120 from theelectrical effects of nearby conductors. In one embodiment, theprocessing system is configured to operate the grid electrode(s) as ashield electrode that may “shield” sensor electrodes 120 from theelectrical effects of nearby conductors, and to guard the sensorelectrodes 120 from grid electrode(s), at least partially reducing theparasitic capacitance between the grid electrode(s) and the sensorelectrodes 120. In one embodiment, a shielding signal is driven onto thegrid electrode(s). The shielding signal may be a ground signal, such asthe system ground or other ground, or any other constant voltage (i.e.,non-modulated) signal. In another embodiment, operating the gridelectrode(s) as a shield electrode may comprise electrically floatingthe grid electrode. In one embodiment, grid electrode(s) are able tooperate as an effective shield electrode while being electrode floateddue to its large coupling to the other sensor electrodes. In otherembodiment, the shielding signal may be referred to as a “guardingsignal” where the guarding signal is a varying voltage signal having atleast one of a similar phase, frequency, and amplitude as the modulatedsignal driven on to the sensor electrodes. In one or more embodiment,routing traces may be shielded from responding to an input object due torouting beneath the grid electrode(s) and/or sensor electrodes 120, andtherefore may not be part of the active sensor electrodes, shown assensor electrodes 120.

In one or more embodiments, capacitive sensing (or input sensing) anddisplay updating may occur during at least partially overlappingperiods. For example, as a common electrode is driven for displayupdating, the common electrode may also be driven for capacitivesensing. In another embodiment, capacitive sensing and display updatingmay occur during non-overlapping periods, also referred to asnon-display update periods. In various embodiments, the non-displayupdate periods may occur between display line update periods for twodisplay lines of a display frame and may be at least as long in time asthe display update period. In such embodiments, the non-display updateperiod may be referred to as a “long horizontal blanking period,” “longh-blanking period” or a “distributed blanking period,” where theblanking period occurs between two display updating periods and is atleast as long as a display update period. In one embodiment, thenon-display update period occurs between display line update periods ofa frame and is long enough to allow for multiple transitions of thetransmitter signal to be driven onto the sensor electrodes 120. In otherembodiments, the non-display update period may comprise horizontalblanking periods and vertical blanking periods. Processing system 110may be configured to drive sensor electrodes 120 for capacitive sensingduring any one or more of or any combination of the differentnon-display update times. Synchronization signals may be shared betweensensor module 310 and display driver module 320 to provide accuratecontrol of overlapping display updating and capacitive sensing periodswith repeatably coherent frequencies and phases. In one embodiment,these synchronization signals may be configured to allow the relativelystable voltages at the beginning and end of the input sensing period tocoincide with display update periods with relatively stable voltages(e.g., near the end of a input integrator reset time and near the end ofa display charge share time). A modulation frequency of a modulated ortransmitter signal may be at a harmonic of the display line update rate,where the phase is determined to provide a nearly constant chargecoupling from the display elements to the receiver electrode, allowingthis coupling to be part of the baseline image.

The sensor module 310 includes circuitry configured to receive resultingsignals with the sensor electrodes 120 and/or grid electrode(s)comprising effects corresponding to the modulated signals or thetransmitter signals during periods in which input sensing is desired.The sensor module 310 may determine a position of the input object inthe sensing region 170 or may provide a signal including informationindicative of the resulting signal to another module or processor, forexample, a determination module 330 or a processor of an associatedelectronic device 150 (i.e., a host processor), for determining theposition of the input object in the sensing region 170.

The display driver module 320 may be included in or separate from theprocessing system 110. The display driver module 320 includes circuitryconfigured to provide display image update information to the display ofthe display device 160 during non-sensing (e.g., display updating)periods.

In one embodiment, the processing system 110 comprises a firstintegrated controller comprising the display driver module 320 and atleast a portion of the sensor module 310 (i.e., transmitter moduleand/or receiver module). In another embodiment, the processing system110 comprises a first integrated controller comprising the displaydriver module 320 and a second integrated controller comprising thesensor module 310. In yet another embodiment, the processing systemcomprises a first integrated controller comprising display driver module320 and a first portion of the sensor module 310 (e.g., one of atransmitter module and a receiver module) and a second integratedcontroller comprising a second portion of the sensor module 310 (e.g.,the other one of the transmitter and receiver modules). In thoseembodiments comprising multiple integrated circuits, a synchronizationmechanism may be coupled between them, configured to synchronize displayupdating periods, sensing periods, transmitter signals, display updatesignals, and the like.

As mentioned above, in some embodiments a determination module 330 maybe configured to determine a position of the input object in the sensingregion 170. The determination module 330 may be further configured toperform other functions related to coordinating the operation of variouscomponents of the processing system 110. In an alternate embodiment,some or all of the functionality attributed to the determination module330 may be provided by a processor external to the processing system 110(e.g., a host processor of an associated electronic system).

Exemplary Arrangements For Input Device Receiver With Delta-SigmaModulator

FIG. 4 illustrates a block diagram of an exemplary input device,according to one embodiment. More specifically, input device 400comprises a processing system 110 coupled with a plurality of sensorelectrodes 120-1 to 120-n. Although described using different referencenumbers, it will be noted that input device 400 may include variousfeatures of the input device 100 discussed above.

The processing system 110 comprises a plurality of k receivers 401-1 to401-k, each of which is configured to receive signals from the sensorelectrodes 120-1 to 120-n. As shown, the receiver 401-1 is configured toreceive a signal 402 from the sensor electrode 120-1. In someembodiments, the receivers 401-1 to 401-k are provided as AFEs of theprocessing system 110, and may include further signal conditioningcircuitry. While discussed specifically with respect to a plurality ofsensor electrodes 120-1 to 120-n, the techniques discussed herein mayalso be used with other arrangements of sensor electrodes (e.g., thepluralities of sensor electrodes 205, 215 of FIG. 2). Furthermore, thereceivers 401-1 to 401-k may be used to receive signals within absolutecapacitive and transcapacitive sensing implementations.

The receiver 401-1 comprises a current conveyor 405 and a mixer 410. Thecurrent conveyor 405 is configured to receive signal 402 and to mirror acurrent of the signal 402 to the output of the current conveyor 405. Thecurrent conveyor 405 may have any suitable gain value. The mixer 410receives the mirrored current from the current conveyor 405 anddownconverts the current from RF frequencies to approximately directcurrent (DC) levels (i.e., having substantially no frequency component).The mixer 410 may have any suitable implementation, such as asquare-wave mixer, harmonic rejection mixer, or sinusoidal mixer.

The current conveyor 405 and mixer 410 operate to produce a processedsignal 412 based on the received signal 402. The processed signal 412may be in the form of a fully-differential output, a pseudo-differentialoutput, or a single-ended output. In one embodiment, the sensorelectrode 120-1 provides a single-ended signal 402 to the currentconveyor 405 and the mixer 410 outputs a fully-differential processedsignal 412.

The receiver 401-1 further comprises a delta-sigma modulator 415 and adigital filter 435. Generally, the delta-sigma modulator 415 operates toencode the processed signal 412 using relatively high-frequencydelta-sigma modulation, and the digital filter 435 is applied to form ahigher resolution, but lower sample frequency, digital output. Thedigital filter 435 may have any suitable implementation. For example,the digital filter 435 may be a finite impulse response (FIR) filter oran infinite impulse response (IIR) filter. In some embodiments, thedigital filter 435 is a low-pass filter. In other embodiments, thedigital filter 435 is a high-pass filter. Further, in some embodimentshaving single-bit quantization, the digital filter 435 does not requiredecimation to be performed, as the single-bit stream can be used toanalyze the frequency spectrum, e.g., using a windowed Fouriertransform. Beneficially, omitting circuitry for performing decimationreduces the area required for the receiver 401-1.

In some embodiments, the delta-sigma modulator 415 is a differentialinput, first-order, continuous time, passive delta-sigma modulator withcommon-mode feedback. Beneficially, the first-order and continuous timeaspects of the delta-sigma modulator 415 require relatively lesscircuitry than higher-order and/or discrete time implementations. Forexample, a continuous time implementation does not require samplingcircuitry to be included outside of the loop of the delta-sigmamodulator 415, resulting in an inherently anti-aliasing implementation.However, in alternate embodiments, the delta-sigma modulator 415comprises a discrete time modulator and/or a higher order thanfirst-order. Further, in alternate embodiments, the delta-sigmamodulator 415 may have single-ended or pseudo-differential inputs.

The delta-sigma modulator 415 further comprises an integrator 420configured to integrate the processed signal 412 to produce anintegration signal 422. The integrator 420 may have an active or passiveimplementation. Generally, a passive implementation comprises solelypassive circuit elements, such as resistances, capacitances, and/orinductances. Generally, an active implementation comprises anoperational amplifier (op-amp) or other active devices capable ofcontrolling electron flow based on a control signal. In someembodiments, integrator 420 comprises a passive integrator, which tendsto require less area while providing improved linear performance, whencompared with an active integrator.

The delta-sigma modulator 415 further comprises a quantizer 425configured to generate a quantization signal 427 based on theintegration signal 422. The quantizer 425 may have any suitablesingle-bit or multiple-bit implementation. In some embodiments,quantizer 425 is a single-bit quantizer that generally requires lessarea than a multiple-bit quantizer. The delta-sigma modulator 415further comprises a feedback digital-to-analog-converter (DAC) 430 thatis controlled based on the quantization signal 427. The feedback DAC 430may have any suitable implementation, such as a return-to-zero (RZ) or anon-return-to-zero (NRZ) DAC. Furthermore, the feedback DAC 430 may beformed as a resistive implementation or a switched capacitor resistor(SCR) network implementation.

In some embodiments having a current conveyor 405, the delta-sigmamodulator 415 comprises a common-mode feedback arrangement configured tomitigate common-mode currents produced by the current conveyor 405.However, in some alternate embodiments, the receiver 401-1 does notinclude the current conveyor 405 and mixer 410. Omitting the currentconveyor 405 (and, in some cases, an associated common-mode feedbackarrangement) and the mixer 410 requires less area for the receiver401-1. In one non-limiting example, a fingerprint sensing implementationmay omit the current conveyor 405 while retaining the common-modefeedback arrangement. Moreover, in these embodiments, the capacitance ofthe sensor electrode 120-1 can be used as the integrator 420, which canfurther reduce required area and power consumption of the receiver401-1. Generally, using the capacitance of sensor electrode 120-1 forthe integrator 420 tends to reduce the oversampling ratio of thedelta-sigma modulator 415 for the same sampling frequency. In somecases, the performance of the delta-sigma modulator 415 is stillacceptable, despite the reduced oversampling ratio. In one embodiment,the delta-sigma modulator 415 is increased to a second-order (or higherorder) implementation to mitigate the decreased performance resultingfrom the reduced oversampling ratio.

In some embodiments, the receiver 401-1 is suitable for performingfingerprint sensing. Generally, fingerprint sensing is performed usingdifferential sensor measurements in order to improve performance withrespect to interference, while location sensing is typically performedusing single-ended measurements. In these embodiments, the relativelylow-impedance input stage comprising current conveyor 405 may bereplaced with a high-impedance input stage (e.g., a transconductor). Forexample, the transconductor may be formed using a differential pairconfigured to receive the signal 402, a gain stage configured to amplifythe output voltage of the differential pair, and a transconductanceamplifier to convert the amplified output voltage to a current, which isthen passed to the mixer 410.

FIG. 5 illustrates a schematic block diagram of an exemplary inputdevice, according to one embodiment. More specifically, the arrangement500 illustrates one possible implementation of a receiver 401 of theinput device. It will be noted that elements may be added to and/oromitted from the arrangement 500 based on various features of the inputdevices 100, 400 discussed above.

A sensor electrode 120 is coupled with the receiver 401. The sensorelectrode 120 is represented using a single-pole model comprising aresistance R_(sensor) and capacitance C_(sensor). While the sensorelectrode 120 can exhibit more complex behavior in practice, asingle-pole model provides a reasonably good approximation for purposesof this description. The sensor electrode 120 provides a signal 402 intoan inverting terminal of an amplifier 502 having unity gain. Theamplifier 502 is included as part of the current conveyor 405, whichfurther comprises current mirrors 504, 506 that are configured toproduce a scaled copy of the input current I_(in) of the amplifier 502.The input current I_(in) is generally produced through application ofthe reference voltage V_(tx) to the non-inverting terminal of theamplifier 502, which in turn controls the voltage at the invertingterminal to apply the voltage across the sensor electrode 120. The inputcurrent I_(in) generally includes the capacitive effects of an inputdevice relative to the sensor electrode 120. The current mirrors 504,506 each scale the input current I_(in) by a factor A, and the scaledcurrents (A·I_(in)) are provided to mixer 410.

Mixer 410 comprises switches 508, 510 operable to downconvert the scaledcurrents from radio frequency (RF) frequencies to approximately directcurrent (DC) values. In one embodiment, the mixer 410 effectivelyperforms a polarity-switching function responsive to control signalsprovided to the switches 508, 510. The mixer 410 is configured toprovide the processed signal 412 to fully-differential input nodes ofthe delta-sigma modulator 415. Generally, the processed signal 412comprises continuous time output signals I_(in+)(t), I_(in−)(t)respectively provided to positive and negative input nodes of thedelta-sigma modulator 415.

As shown, the delta-sigma modulator 415 includes a common-mode feedbackarrangement 512 configured to mitigate a common-mode current produced bythe current conveyor 405. Generally, the common-mode feedbackarrangement 512 operates to keep the voltages on the input nodesV_(inp)(t), V_(inm)(t) centered around a common-mode voltage V_(CM). Thecommon-mode feedback arrangement 512 comprises a transconductanceamplifier 514 having a gain G_(m) and coupled with the positive andnegative input nodes of the delta-sigma modulator 415. In someembodiments, the transconductance amplifier 514 is a class A amplifieror a class AB amplifier. The transconductance amplifier 514 is furtherconfigured to receive a reference voltage V_(ref). In some embodiments,V_(ref) is the common-mode voltage V_(CM) or is approximately V_(DD)/2.The output of the transconductance amplifier 514 controls the currentprovided by current mirrors I_(cmp+)(t), I_(cmp−)(t) to the respectivepositive and negative input nodes. The common-mode feedback arrangement512 further comprises current mirrors I_(cmn+)(t), I_(cmn−)(t) coupledwith the respective positive and negative input nodes.

In some embodiments, the common-mode feedback arrangement 512 furthercomprises chopping circuitry 516 p, 516 n configured to mitigate alow-frequency noise of the current mirrors I_(cmp+)(t), I_(cmp−)(t),I_(cmn+)(t), I_(cmn−)(t). For example, the chopping circuitry 516 p, 516n may be configured to remove a (1/f) noise of the current mirrors,while higher frequency noise is typically removed at a later stage bythe digital filter 435. In some alternate embodiments, the common-modefeedback arrangement 512 is omitted.

The common-mode feedback arrangement 512 further comprises capacitancesC2, C3 which are configured to prevent voltages on the input nodesV_(inp)(t), V_(inm)(t) from reaching rail voltages. The capacitances C2,C3 present a common-mode impedance that is seen by the currents outputfrom the mixer 410 (as shown, I_(in+)(t), I_(in−)(t)). Further, thecapacitances C2, C3 enable function of the receiver 401 in that theoutput of the current conveyor 405 is only connected to one of the twoinput nodes of the delta-sigma modulator 415 at a given time.

The delta-sigma modulator 415 further comprises the integrator 420coupled with the positive and negative input nodes. As shown, theintegrator 420 is a passive integrator comprising capacitors C0, C1 andconfigured to produce an integration signal 422 based on the continuoustime signals I_(in+)(t), I_(in−)(t) on the positive and negative inputnodes of the delta-sigma modulator 415. The reset switch 518 isconfigured to reset the delta-sigma modulator 415 to ensure that thedelta-sigma modulator 415 begins sensing periods from a same bias point.The integrator 420 is coupled with input terminals of a single-bitquantizer 425. The quantizer 425 receives a clock signal (CLK) having afrequency suitable for achieving a relatively large oversampling ratio.Some non-limiting examples of “large” oversampling ratios are 500-2,000or more. The oversampling ratio, when sufficiently large, causesquantization noise from the quantizer 425 to be shaped such that it isremoved using the digital filter 435 (e.g., a low-pass digital filter).

The output value D of the quantizer 425 (and its inverse) represent aquantization signal 427 that is used to control switches 520 p, 520 n ofa feedback digital-to-analog converter (DAC) 430 of the delta,sigmamodulator 415. In this way, the integrator 420, quantizer 425, andfeedback DAC 430 form a feedback loop of the delta-sigma modulator 415.The feedback DAC 430 further comprises current sources I_(dfp), I_(dfn)that are selectively coupled with the positive or negative input nodesof the delta-sigma modulator 415 based on the quantization signal 427.For example, when the voltage signal comprising the difference ofV_(inp)(t), V_(inm)(t) increases (or expands), the quantization signal427 causes current source I_(dfp) to be connected with the negativeinput node, and causes current source I_(dfn) to be coupled with thepositive input node. In this way, current source I_(dfp) pushes chargeonto the top plate of capacitor C1, increasing the voltage V_(inm)(t).Likewise, current source I_(dfn) pulls charge from the top plate ofcapacitor C0, decreasing the voltage V_(inp)(t) and thus mitigating thevoltage difference between V_(inp)(t) and V_(inm)(t). The feedback DAC430 further includes a “reset” state in which the current sourcesI_(dfp), I_(dfn) are coupled with the reference voltage V_(ref).

In one embodiment, the current sources I_(dfp), I_(dfn) produce areturn-to-zero (RZ) waveform having a 25% duty cycle, which may beadvantageous for reducing intersymbol interference. In alternateembodiments, the current sources I_(dfp), I_(dfn) may provide RZwaveforms with different duty cycles or non-return-to-zero (NRZ)waveforms. Further, although the feedback DAC 430 may have alternateimplementations such as a resistive implementation or a SCR networkimplementation, the depicted implementation of the current sourcesI_(dfp), I_(dfn) generally requires reduced area when compared with thealternate implementations.

Using the various techniques discussed above, the receiver 401 canprovide substantial area savings for an input device, when compared withconventional receiver circuitry. For example, an area required forimplementing an AFE including receiver 401 may be on the order ofone-quarter (25%) the area required for a conventional touch-sensingAFE, or on the order of one-eighth (12.5%) the area required for aconventional fingerprint-sensing AFE. Therefore, more AFEs may beincluded within a given semiconductor area (and cost) to improve inputsensing performance. Alternatively, a given number of AFEs requires lesssemiconductor area (and reduces cost) relative to conventionalimplementations.

The receiver 401 also provides improved sensing performance of the inputdevice. Assuming a limited period is available for acquiring a sensingframe, the receiver 401 offers narrower system bandwidth and improvesinterference performance, as more receivers 401 can be included within agiven semiconductor area and operated in parallel. For example, assumean input device includes 512 sensor electrodes and 64 “conventional”AFEs. If a period of 2 milliseconds (ms) is allotted equally foracquiring a sensing frame, each AFE corresponds to a maximum of 250microseconds (μs) (2 ms×64/512) available for sensing. However, furtherassuming that receiver 401 provides a 4:1 area savings, the 64“conventional” AFEs may be replaced by 256 AFEs, which corresponds to amaximum of 1 ms (2 ms×4×64/512) available for sensing. This 4:1 increasein sensing time can correspond to a 4:1 reduction in system bandwidth,which results in improved interference performance.

Further, AFEs implementing receiver 410 can reduce the total timerequired to acquire a sensing frame, which allows more time for displayupdating (e.g., enabling increased display resolutions) and/or otherprocessing functions. For example, assuming the same sensing parametersfrom the previous example and maintaining the sensing time at 250 μs,then the total amount of time required for acquiring a sensing frame is500 μs. Thus, 1.5 ms of the 2 ms allotted for sensing may be returned tothe display, which may reduce constraints on display timing and signalsettling.

FIG. 6 is an exemplary method of processing signals received from asensor electrode, according to one embodiment. Method 600 is generallyintended to be performed in conjunction with embodiments of receiver401, discussed above with respect to FIG. 4.

Method 600 begins at block 605, where a sensor signal is received at oneor more input nodes from a first sensor electrode of a plurality ofsensor electrodes. In some embodiments, the one or more input nodes areinput nodes of a delta-sigma modulator of the receiver 401. In otherembodiments, the one or more input nodes are inputs nodes of a currentconveyor coupled with the delta-sigma modulator through a mixer. In thiscase, the sensor signal may be a single-ended input to the currentconveyor.

For embodiments including a current conveyor and mixer, at optionalblock 615, a current of the sensor signal is mirrored using a currentconveyor. In some embodiments, the mirrored current is also scaled basedon a gain of current mirrors included in the current conveyor. Atoptional block 625, the mirrored current is provided through a mixer toone or more input nodes of the delta-sigma modulator. At optional block635, using a common-mode feedback circuit coupled with the one or moreinput nodes, a common-mode current produced by the current conveyor ismitigated.

At block 645, a signal based on the sensor signal is integrated toproduce an integration signal. At block 655, the integration signal isquantized. At block 665, a feedback digital-to-analog converter (DAC)coupled with the one or more input nodes is controlled based on thequantization of the integration signal. At block 675, a quantizationnoise is mitigated using a digital filter coupled with the delta-sigmamodulator. Method 600 ends following completion of block 675.

Thus, the embodiments and examples set forth herein were presented inorder to best explain the embodiments in accordance with the presenttechnology and its particular application and to thereby enable thoseskilled in the art to make and use the disclosure. However, thoseskilled in the art will recognize that the foregoing description andexamples have been presented for the purposes of illustration andexample only. The description as set forth is not intended to beexhaustive or to limit the disclosure to the precise form disclosed.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

What is claimed is:
 1. A processing system for an input device, theprocessing system comprising: a mixer configured to: downconvert a firstsignal derived from a sensor signal received by the input device; andoutput a processed signal; a delta-sigma modulator configured to receivethe processed signal, the delta-sigma modulator comprising a quantizer;and a digital filter coupled with an output of the delta-sigma modulatorand configured to mitigate a quantization noise of the quantizer.
 2. Theprocessing system of claim 1, wherein the delta-sigma modulator isincluded in receiver circuitry of the processing system.
 3. Theprocessing system of claim 1, wherein the delta-sigma modulator furthercomprises a differential modulator configured to receive the processedsignal.
 4. The processing system of claim 1, wherein the first signal isa mirrored current signal generated by a current conveyor from thesensor signal.
 5. The processing system of claim 4, wherein thedelta-sigma modulator further comprises a first input node and a secondinput node, the processed signal is received with one of the first inputnode and the second input node of the delta-sigma modulator, and a firstcommon mode capacitor and a second common mode capacitor are coupledbetween the first input node and the second input node.
 6. Theprocessing system of claim 1, wherein the processed signal hassubstantially no frequency component.
 7. The processing system of claim1, wherein the mixer comprises a plurality of switches configured todownconvert the first signal by performing a polarity-switchingfunction.
 8. An input device comprising: a sensor electrode; aprocessing system coupled to the sensor electrode, the processing systemcomprising: a mixer configured to: downconvert a first signal derivedfrom a sensor signal received by the sensor electrode; and output aprocessed signal; a delta-sigma modulator configured to receive theprocessed signal, the delta-sigma modulator comprising a quantizer; anda digital filter coupled with an output of the delta-sigma modulator andconfigured to mitigate a quantization noise of the quantizer.
 9. Theinput device of claim 8, wherein the delta-sigma modulator is includedin receiver circuitry of the processing system.
 10. The input device ofclaim 8, wherein delta-sigma modulator further comprises a differentialmodulator configured to receive the processed signal.
 11. The inputdevice of claim 10, wherein the processing system is further configuredto provide the processed signal comprising continuous time outputsignals to the differential modulator of the delta-sigma modulator. 12.The input device of claim 8, wherein the first signal is a mirroredcurrent signal generated by a current conveyor from the sensor signal.13. The input device of claim 8, wherein the processed signal hassubstantially no frequency component.
 14. The input device of claim 8,wherein the delta-sigma modulator further comprises a first input nodeand a second input node, the processed signal is received with one ofthe first input node and the second input node of the delta-sigmamodulator, and a first common mode capacitor and a second common modecapacitor are coupled between the first input node and the second inputnode.
 15. The input device of claim 8, wherein the mixer comprises aplurality of switches configured to downconvert the first signal byperforming a polarity-switching function.
 16. A method comprising:generating, using a mixer, a processed signal by downconverting a firstsignal derived from a sensor signal received by an input device;quantizing, using a delta-sigma modulator, an integration signal,wherein the integration signal is based on the processed signal; andmitigating, using a digital filter, quantization noise of thedelta-sigma modulator.
 17. The method of claim 16, further comprising:controlling a feedback digital-to-analog converter (DAC) based on thequantization of the integration signal, the feedback DAC coupled withone or more input nodes of the delta-sigma modulator.
 18. The method ofclaim 16, wherein the processed signal has substantially no frequencycomponent.
 19. The method of claim 16, wherein generating the processedsignal by downconverting the first signal comprises controlling aplurality of switches to perform a polarity-switching function.
 20. Themethod of claim 16, further comprising receiving the processed signalwith one of a first input node and a second node of the delta-sigmamodulator, and wherein a first common mode capacitor and a second commonmode capacitor are coupled between the first input node and the secondinput node.